title: The incidence and clinical implication of sputum with positive acid-fast bacilli smear but negative in mycobacterial culture in a tertiary referral hospital in South Korea.
abstract: Although it is not rare to find sputum that is positive acid-fast bacilli (AFB) smear but subsequent culture fails to isolate mycobacteria in clinical practice, the incidence and clinical implication of those sputa from new patients has not been clearly elucidated. The aim of this study was to determine the incidence and clinical implication of sputum with positive AFB smear but negative in mycobacterial culture. All sputa that were positive AFB smear requested during diagnostic work up for new patients visiting Seoul National University Hospital from 1 January 2005 through 31 December 2006 were included. Sputa producing a positive AFB smear but negative mycobacterial culture were classified into one of four categories: laboratory failure to isolate mycobacteria, false positive AFB smear, pathogen may show a positive AFB smear other than mycobacteria, and indeterminate results. Out of 447 sputa with a positive AFB smear, 29 (6.5%) failed to culture any organism. Among these 29 sputa, 18 were caused by laboratory failure to isolate mycobacteria, six were false positive smears, and five indeterminate. Although most sputum with a positive AFB smear but negative culture could be classified as a laboratory failure, clinicians should consider the possibility of false positive AFB smear.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Jae Seok
authors.initials: JS
authors.lastname: Lee
authors.forename: Eui-Chong
authors.initials: EC
authors.lastname: Kim
authors.forename: Sei Ick
authors.initials: SI
authors.lastname: Joo
authors.forename: Sang-Min
authors.initials: SM
authors.lastname: Lee
authors.forename: Chul-Gyu
authors.initials: CG
authors.lastname: Yoo
authors.forename: Young Whan
authors.initials: YW
authors.lastname: Kim
authors.forename: Sung Koo
authors.initials: SK
authors.lastname: Han
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Shim
authors.forename: Jae-Joon
authors.initials: JJ
authors.lastname: Yim
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015373:Bacterial Typing Techniques; D001431:Bacteriological Techniques; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D015994:Incidence; D007723:Korea; D008297:Male; D008875:Middle Aged; D009161:Mycobacterium / Q000378:metabolism*; D012189:Retrospective Studies; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology